The present invention relates to a magnet assembly for use in a magnetic resonance imaging system used in medical diagnosis applications.
As shown in FIG. 8 of the accompanying drawings, an MRI (magnetic resonance imaging system) has four ring-shaped magnets M defining a projection region space centrally therein and spaced at axial intervals. The magnets M serve to produe a uniform static magnetic field in the projection region space in which a portion (such as the head, for exampe), to be imaged, of a human body P on a bed is placed. The MRI system also has two curved high-frequency coils HC disposed around the portion to be imaged. High-frequency pulses are applied to the high-frequency coils HC to enable the same to generate an MR signal which will be detected by the same high-frequency coils HC. Each of the magnets M comprises a winding or coil in the form of an air core coil.
The static magnetic field is required to be intensive enough to produce mangnetic resonance and also to keep the projection region space uniform. Since the conventional magnet assembly is large in size and heavy, it cannot be transported and installed while it is in the assembled condition (i.e., capable of operation). Therefore, the magnet assembly is carried to the installation site while it is in the disassembled condition. At the installation site, the magnet assembly is put together, and the air core coils for generating the static magnetic field are positionally adjusted in X-, Y-, and Z-axis directions with respect to the axis of an outer cylindrical casing in which the coils are to be housed.
Inasmuch as the outer cylindrical casing is constructed as a single body, the process of attaching the coils to the outer cylindrical casing and the process of accurately positinally adjusting the coils in the above three directions, procedures which greatly affect the requirements to be met by the static magnetic field, must be carried out at the time of installing the magnet assembly. The assembling process is complex because the number of required parts is large and the structure is complicated. Furthermore, it is difficult to reassume the coil positions prior to the disassembling of the magnet assembly.